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Thu, 16 Jul 2020 15:04:51 +0000 (UTC) Subject: Re: [PATCH v7 17/47] block: Re-evaluate backing file handling in reopen To: Andrey Shinkevich , qemu-block@nongnu.org References: <20200625152215.941773-1-mreitz@redhat.com> <20200625152215.941773-18-mreitz@redhat.com> From: Max Reitz Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: Date: Thu, 16 Jul 2020 17:04:50 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mreitz@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="ZnjDr1SOOMUnVl6lukaiM0BQ2IVJGC4Xg" Received-SPF: pass client-ip=205.139.110.120; envelope-from=mreitz@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/15 19:36:06 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --ZnjDr1SOOMUnVl6lukaiM0BQ2IVJGC4Xg Content-Type: multipart/mixed; boundary="I1WAJ9lh6Mlijs0OtbCIudsgfa7OzgRM0" --I1WAJ9lh6Mlijs0OtbCIudsgfa7OzgRM0 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 10.07.20 21:42, Andrey Shinkevich wrote: > On 25.06.2020 18:21, Max Reitz wrote: >> Reopening a node's backing child needs a bit of special handling because >> the "backing" child has different defaults than all other children >> (among other things).=C2=A0 Adding filter support here is a bit more >> difficult than just using the child access functions.=C2=A0 In fact, we = often >> have to directly use bs->backing because these functions are about the >> "backing" child (which may or may not be the COW backing file). >> >> Signed-off-by: Max Reitz >> --- >> =C2=A0 block.c | 46 ++++++++++++++++++++++++++++++++++++++-------- >> =C2=A0 1 file changed, 38 insertions(+), 8 deletions(-) >> >> diff --git a/block.c b/block.c >> index 712230ef5c..8131d0b5eb 100644 >> --- a/block.c >> +++ b/block.c >> @@ -4026,26 +4026,56 @@ static int >> bdrv_reopen_parse_backing(BDRVReopenState *reopen_state, >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >> =C2=A0 +=C2=A0=C2=A0=C2=A0 /* >> +=C2=A0=C2=A0=C2=A0=C2=A0 * Ensure that @bs can really handle backing fi= les, because we are >> +=C2=A0=C2=A0=C2=A0=C2=A0 * about to give it one (or swap the existing o= ne) >> +=C2=A0=C2=A0=C2=A0=C2=A0 */ >> +=C2=A0=C2=A0=C2=A0 if (bs->drv->is_filter) { >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* Filters always have a fil= e or a backing child */ >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (!bs->backing) { >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 erro= r_setg(errp, "'%s' is a %s filter node that does not >> support a " >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 "backing ch= ild", bs->node_name, >> bs->drv->format_name); >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 retu= rn -EINVAL; >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >> +=C2=A0=C2=A0=C2=A0 } else if (!bs->drv->supports_backing) { >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 error_setg(errp, "Driver '%s= ' of node '%s' does not support >> backing " >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 "files", bs->drv->format_name, bs->= node_name); >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return -EINVAL; >> +=C2=A0=C2=A0=C2=A0 } >> + >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * Find the "actual" backing file by= skipping all links that point >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * to an implicit node, if any (e.g.= a commit filter node). >> +=C2=A0=C2=A0=C2=A0=C2=A0 * We cannot use any of the bdrv_skip_*() funct= ions here because >> +=C2=A0=C2=A0=C2=A0=C2=A0 * those return the first explicit node, while = we are looking for >> +=C2=A0=C2=A0=C2=A0=C2=A0 * its overlay here. >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */ >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 overlay_bs =3D bs; >> -=C2=A0=C2=A0=C2=A0 while (backing_bs(overlay_bs) && backing_bs(overlay_= bs)->implicit) { >> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 overlay_bs =3D backing_bs(ov= erlay_bs); >> +=C2=A0=C2=A0=C2=A0 while (bdrv_filter_or_cow_bs(overlay_bs) && >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 bdrv_filte= r_or_cow_bs(overlay_bs)->implicit) >> +=C2=A0=C2=A0=C2=A0 { >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 overlay_bs =3D bdrv_filter_o= r_cow_bs(overlay_bs); >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >=20 > I believe that little optimization would work properly: >=20 >=20 > for (BlockDriverState *below_bs =3D bdrv_filter_or_cow_bs(overlay_bs); > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 below_bs && below_bs->implicit; > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 below_bs =3D bdrv_filter_or_cow_bs(o= verlay_bs)) { > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 overlay_bs =3D below_bs; > } Looks good, thanks. >> =C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* If we want to replace the backi= ng file we need some extra >> checks */ >> -=C2=A0=C2=A0=C2=A0 if (new_backing_bs !=3D backing_bs(overlay_bs)) { >> +=C2=A0=C2=A0=C2=A0 if (new_backing_bs !=3D bdrv_filter_or_cow_bs(overla= y_bs)) { >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* Check for impl= icit nodes between bs and its backing file */ >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (bs !=3D overl= ay_bs) { >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0 error_setg(errp, "Cannot change backing link if '%s' has " >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 "a= n implicit backing file", bs->node_name); >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0 return -EPERM; >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* Check if the backing link= that we want to replace is >> frozen */ >> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (bdrv_is_backing_chain_fr= ozen(overlay_bs, >> backing_bs(overlay_bs), >> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0 errp)) { >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * Check if the backing= link that we want to replace is frozen. >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * Note that >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * bdrv_filter_or_cow_c= hild(overlay_bs) =3D=3D overlay_bs->backing, >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * because we know that= overlay_bs =3D=3D bs, and that @bs >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * either is a filter t= hat uses ->backing or a COW format BDS >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * with bs->drv->suppor= ts_backing =3D=3D true. >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */ >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (bdrv_is_backing_chain_fr= ozen(overlay_bs, >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0 >> child_bs(overlay_bs->backing), errp)) > What would be wrong with bdrv_filter_or_cow_bs(overlay_bs) here? As the comment says, it=E2=80=99s the same thing. I prefer ->backing here, because this function is about reopening the ->backing child. >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 { >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0 return -EPERM; >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 reopen_state->rep= lace_backing_bs =3D true; >> @@ -4196,7 +4226,7 @@ int bdrv_reopen_prepare(BDRVReopenState >> *reopen_state, BlockReopenQueue *queue, >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * its metadata. Otherwise the 'back= ing' option can be omitted. >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */ >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (drv->supports_backing && reopen_state= ->backing_missing && >> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 (backing_bs(reopen_state->bs= ) || >> reopen_state->bs->backing_file[0])) { > =3D BlockDriverState* >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 (reopen_state->bs->backing |= | >> reopen_state->bs->backing_file[0])) { >=20 > =3D BdrvChild* >=20 > Are we OK with that? Sure, the question is whether it=E2=80=99s non-NULL, and BdrvChild.bs is al= ways non-NULL. 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